U.S. patent number 8,288,198 [Application Number 12/300,459] was granted by the patent office on 2012-10-16 for low temperature deposition of phase change memory materials.
This patent grant is currently assigned to Advanced Technology Materials, Inc.. Invention is credited to Thomas H. Baum, Tianniu Chen, Bryan C. Hendrix, William Hunks, Jeffrey F. Roeder, Gregory T. Stauf, Matthias Stender, Chongying Xu.
United States Patent |
8,288,198 |
Roeder , et al. |
October 16, 2012 |
**Please see images for:
( Certificate of Correction ) ** |
Low temperature deposition of phase change memory materials
Abstract
A system and method for forming a phase change memory material
on a substrate, in which the substrate is contacted with precursors
for a phase change memory chalcogenide alloy under conditions
producing deposition of the chalcogenide alloy on the substrate, at
temperature below 350.degree. C. with the contacting being carried
out via chemical vapor deposition or atomic layer deposition.
Various tellurium, germanium and germanium-tellurium precursors are
described, which are useful for forming GST phase change memory
films on substrates.
Inventors: |
Roeder; Jeffrey F. (Brookfield,
CT), Baum; Thomas H. (New Fairfield, CT), Hendrix; Bryan
C. (Danbury, CT), Stauf; Gregory T. (New Milford,
CT), Xu; Chongying (New Milford, CT), Hunks; William
(Waterbury, CT), Chen; Tianniu (Rocky Hill, CT), Stender;
Matthias (New Milford, CT) |
Assignee: |
Advanced Technology Materials,
Inc. (Danbury, CT)
|
Family
ID: |
38694573 |
Appl.
No.: |
12/300,459 |
Filed: |
March 12, 2007 |
PCT
Filed: |
March 12, 2007 |
PCT No.: |
PCT/US2007/063832 |
371(c)(1),(2),(4) Date: |
December 22, 2008 |
PCT
Pub. No.: |
WO2007/133837 |
PCT
Pub. Date: |
November 22, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090124039 A1 |
May 14, 2009 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60800102 |
May 12, 2006 |
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Current U.S.
Class: |
438/99; 438/622;
438/579; 438/602; 257/E21.438; 257/410; 257/379; 257/368 |
Current CPC
Class: |
C23C
16/45553 (20130101); C23C 16/305 (20130101); C07F
7/30 (20130101); H01L 51/0002 (20130101) |
Current International
Class: |
H01L
51/40 (20060101) |
References Cited
[Referenced By]
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Aug 2002 |
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JP |
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May 2005 |
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Primary Examiner: Lee; Kyoung
Attorney, Agent or Firm: Hultquist, PLLC Hultquist; Steven
J. Chappuis; Maggie
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a U.S. national phase under the provisions of
35 U.S.C. .sctn.371 of International Application No. PCT/US07/63832
filed Mar. 12, 2007, which in turn claims priority of U.S.
Provisional Patent Application No. 60/800,102 filed May 12, 2006.
The disclosures of such international application and U.S. priority
application are hereby incorporated herein by reference in their
respective entireties, for all purposes.
Claims
What is claimed is:
1. A method of forming a GeSbTe semiconductor, comprising
depositing a film of GeSbTe semiconductor material by CVD or ALD,
and doping same with nitrogen, wherein said doping comprises at
least one of (i) use of the vaporizable liquid, and (ii) pulsing of
nitrogen dopant, optionally with purging between pulses.
2. The method of claim 1, wherein said doping comprises use of a
reactant gas.
3. The method of claim 2, wherein said reactant gas comprises
ammonia.
4. The method of claim 1, wherein said doping comprises use of a
vaporizable liquid.
5. The method of claim 4, wherein said vaporizable liquid comprises
an amine liquid.
6. The method of claim 2, wherein the reactant gas is introduced as
a co-reactant with precursors during formation of said film.
7. The method of claim 2, wherein the reactant gas is introduced as
a carrier gas for precursors during formation of said film.
8. The method of claim 1, wherein the doping comprises pulsing of
nitrogen dopant, optionally with purging between pulses.
9. The method of claim 1, wherein the doping comprises
incorporation of nitrogen from a nitrogen-containing precursor in
the formation of the film.
10. A method of forming a GeSbTe film on a substrate, comprising
use of a germanium complex comprising ligand selected from the
group consisting of isopropyl, isobutyl, benzyl, allyl, alkylamino,
nitriles, and isonitriles, in chemical vapor deposition or atomic
layer deposition.
11. The method of claim 10, wherein said chemical vapor deposition
or atomic layer deposition is carried out at temperature below
350.degree. C.
12. The method of claim 10, wherein the germanium complex comprises
isopropyl ligand.
13. The method of claim 10, wherein the germanium complex comprises
isobutyl ligand.
14. The method of claim 10, wherein the germanium complex comprises
benzyl ligand.
15. The method of claim 10, wherein the germanium complex comprises
allyl ligand.
16. The method of claim 10, wherein the germanium complex comprises
alkylamino ligand.
17. The method of claim 10, wherein the germanium complex comprises
nitrile ligand.
18. The method of claim 10, wherein the germanium complex comprises
isonitrile ligand.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to low temperature deposition of
phase change memory materials, by deposition techniques such as
chemical vapor deposition and atomic layer deposition, to form
microelectronic device structures.
2. Description of the Related Art
Phase Change Memory (PCM) refers to a novel memory technology based
on chalcogenide materials that undergo a phase change via a heater
and are read out as "0" or "1" based on their electrical
resistivity, which changes in correspondence to whether the phase
change material in the cell is in the crystalline or amorphous
phase.
The chalcogenide materials used in PCM comprise a large number of
binary, ternary, and quaternary alloys of a number of metals and
metalloids. Examples include GeSbTe, GeSbInTe, and many others. As
contained herein, the identification of compounds such as GeSbTe
and GeSbInTe without appertaining stoichiometric coefficients or
values will be understood as a general representation inclusive of
all forms of such compounds containing the specified elements, and
inclusive of all appertaining stoichiometric coefficients and
values. For example, the reference to GeSbInTe includes
Ge.sub.2Sb.sub.2Te.sub.5, as well as all other stoichiometric forms
of such compound GeSbInTe.
PCM devices require relatively pure chalconide material alloys,
with well controlled composition. Current processes for making PCM
devices utilize physical vapor deposition to deposit thin films of
these chalconide materials. The thick planar structures of the
current generation are well-served by PVD.
As device geometries shrink, the chalconide material must be
deposited into vias in order to control the phase transition and
the necessary heat transfer. Such implementation of chalconide
materials can also be beneficial in improving reliability of small
volume devices.
A major deficiency in the current art is the requirement of high
deposition temperatures needed for conventionally employed alkyl
(e.g., Me.sub.3Sb, Me.sub.2Te) or halide sources. These
temperatures are typically well in excess of 300.degree. C., and
may for example be on the order of 500.degree. C. Such high
temperatures substantially exceed the thermal budget for device
integration and can result in the evaporation of the chalcogenide,
rendering the product PCM device deficient or even useless for its
intended purpose.
The art continues to seek improvements in the art of PCM devices,
including improvements in manufacturing techniques and improved
precursors useful for forming memory device structures.
SUMMARY OF THE INVENTION
The present invention relates to systems and processes for
deposition of phase change memory material on substrates, for
fabrication of a phase change memory devices.
The invention relates in one aspect to a method of forming a phase
change memory material on a substrate, comprising contacting the
substrate with precursors for a phase change memory chalcogenide
alloy under conditions producing deposition of the chalcogenide
alloy on the substrate, wherein such conditions comprise
temperature below 350.degree. C. and such contacting comprises
chemical vapor deposition or atomic layer deposition.
In another aspect, the invention relates to a method of forming a
germanium-antimony-tellurium phase change memory material on a
substrate, comprising contacting the substrate with precursors for
a phase change memory germanium-antimony-tellurium alloy under
conditions producing deposition of the germanium-antimony-tellurium
alloy on the substrate, wherein such conditions comprise
temperature below 350.degree. C. and such contacting comprises
chemical vapor deposition or atomic layer deposition, with the
precursors comprising at least one halide precursor.
Yet another aspect of the invention relates to a system for
fabricating a phase change memory device including a phase change
memory material on a substrate, such system including a deposition
tool adapted to receive precursors from precursor supply packages,
and precursor supply packages containing precursors for forming a
phase change memory chalcogenide alloy under conditions producing
deposition of the chalcogenide alloy on the substrate, wherein such
deposition tool is adapted for chemical vapor deposition or atomic
layer deposition operation under conditions comprising deposition
temperature below 350.degree. C.
A further aspect of the invention relates to a system for
fabricating a germanium-antimony-tellurium phase change memory
device including a germanium-antimony-tellurium phase change memory
material on a substrate, such system comprising a deposition tool
adapted to receive precursors from precursor supply packages, and
precursor supply packages containing germanium, antimony and
tellurium precursors for forming a germanium-antimony-tellurium
phase change memory chalcogenide alloy under conditions producing
deposition of the chalcogenide alloy on the substrate, wherein the
deposition tool is adapted for chemical vapor deposition or atomic
layer deposition operation under conditions comprising deposition
temperature below 350.degree. C., and at least one of the precursor
supply packages contains a halide precursor.
Additional aspects of the invention relate to PCM films formed in
accordance with the present invention; corresponding devices;
tellurium complexes, germanium complexes, germanium tellurides, and
processes utilizing same for forming GST films; compositions
including combinations of precursors for forming PCM films; and
packaged precursors adapted for coupling to a deposition tool
comprising such compositions, as hereinafter more fully
described.
Other aspects, features and embodiments of the invention will be
more fully apparent from the ensuing disclosure and appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a phase change memory
device comprising a phase change memory material film formed on a
substrate, according to one embodiment of the invention.
FIG. 2 is a schematic representation of a process installation
including a deposition tool for depositing a phase change memory
material on a substrate in accordance with one embodiment of the
invention, from respective precursor supply packages of germanium
precursor, antimony precursor and tellurium precursor.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
THEREOF
The present invention relates to deposition of phase change memory
materials to form PCM devices.
More specifically, the invention in one aspect relates to
chalcogenide alloys, and to their low temperature deposition e.g.,
by chemical vapor deposition (CVD) or atomic layer deposition
(ALD), to form PCM devices. CVD and ALD methods are employed in the
practice of the present invention to achieve scalability to large
area wafers and for composition control. Preferred chalconide
alloys include alloys including two or more of germanium, antimony
and tellurium.
As used herein, the term "low temperature" means a temperature
below 350.degree. C. The temperature at which the PCM material is
deposited is preferably less than 300.degree. C., more preferably
less than 250.degree. C. and most preferably less than 225.degree.
C.
In one aspect, the invention relates to a method of forming a phase
change memory material on a substrate, comprising contacting the
substrate with precursors for a phase change memory chalcogenide
alloy under conditions producing deposition of the chalcogenide
alloy on the substrate, wherein such conditions comprise
temperature below 350.degree. C. and such contacting comprises
chemical vapor deposition or atomic layer deposition.
The advantages of chemical vapor deposition and atomic layer
deposition at low deposition temperature in the fabrication of PCM
devices include substantial improvement of read/re-write times in
small devices, as a result of the high conformality of the
deposited PCM material.
Such method may further include fabricating said phase change
memory material is into a phase change memory device.
The chalcogenide metal and metal alloy precursors that are
advantageously used for forming PCM films and devices include:
(i) butyl- and propyl-substituted alkyl hydrides of the formula
R.sub.xMH.sub.y-x wherein: R is butyl or propyl, with R preferably
being t-butyl or isopropyl; M is a metal having an oxidation state
y, e.g., Ge, Sb or Te; x>1; and (y-x) may have a zero value;
(ii) butyl- and propyl-substituted alkyl halides of the formula
R.sub.xMX.sub.y-x wherein: R is butyl or propyl, with R preferably
being t-butyl or isopropyl; X is F, Cl, or Br; M is a metal having
an oxidation state y, e.g., Ge, Sb or Te; x>1; and (y-x) may
have a zero value; (iii) digermanes of the formula
Ge.sub.2(R.sup.1).sub.6 wherein the R.sup.1 substituents are the
same as or different from one another, and each R.sup.1 is
independently selected from among H, C.sub.1-C.sub.8 alkyl,
C.sub.1-C.sub.8 fluroalkyl, C.sub.6-C.sub.12 aryl, C.sub.6-C.sub.12
fluoroaryl, C.sub.3-C.sub.8 cycloalkyl, and C.sub.3-C.sub.8
cyclo-fluoroalkyl, with illustrative digermanes including
Ge.sub.2H.sub.6, Ge.sub.2Me.sub.6, Ge.sub.2Et.sub.6.
Ge.sub.2iPr.sub.6, Ge.sub.2tBu.sub.6, Ge.sub.2(SiMe.sub.3).sub.6
and Ge.sub.2Ph.sub.6, wherein Me=methyl, Et=ethyl, iPr=isopropyl,
Bu=butyl and Ph=phenyl; (iv) digermanes of the formula
Ge.sub.2(R.sup.1).sub.4 wherein the R.sup.1 substituents are the
same as or different from one another, and each R.sup.1 is
independently selected from among H, C.sub.1-C.sub.8 alkyl,
C.sub.1-C.sub.8 fluroalkyl, C.sub.6-C.sub.12 aryl, C.sub.6-C.sub.12
fluoroaryl, C.sub.3-C.sub.8 cycloalkyl, and C.sub.3-C.sub.8
cyclo-fluoroalkyl, with illustrative digermanes including
Ge.sub.2Ph, wherein Ph=phenyl; (v) ring compounds including Ge as a
ring constituent, e.g., five-member ring compounds; (vi) Ge(II)
compounds of the formula Ge(Cp(R.sup.2).sub.5).sub.2 wherein Cp is
cyclopentadienyl having R.sup.2 substituents on the
cyclopentadienyl ring carbon atoms, wherein the R.sup.2
substituents are the same as or different from one another, and
each R.sup.2 is independently selected from among H,
C.sub.1-C.sub.8 alkyl, C.sub.1-C.sub.8 fluoroalkyl, C.sub.1-C.sub.8
alkylamino, C.sub.6-C.sub.12 aryl, C.sub.6-C.sub.12 fluoroaryl,
C.sub.3-C.sub.8 cycloalkyl, and C.sub.3-C.sub.8 cyclo-fluoroalkyl;
(vii) Ge(II) compounds of the formula Ge(R.sup.3).sub.2, wherein
the R.sup.3 substituents are the same as or different from one
another, and each R.sup.3 is independently selected from among
silyl, silylalkyl and substituted silylalkyl, e.g., wherein each
R.sup.3 is --CH(SiMe.sub.3).sub.2; (viii) Sb compounds of the
formula Sb(R.sup.4).sub.3 wherein R.sup.4 is phenyl, or substituted
phenyl whose substituent(s) on the phenyl ring are independently
selected from among H, C.sub.1-C.sub.8 alkyl, and C.sub.1-C.sub.8
fluroalkyl; (ix) Sb and Te analogs of germanium compounds (iii),
(iv), (v), (vi), and (vii); (x) Ge and Te analogs of antimony
compounds (viii); and (xi) GeI.sub.4, SbI.sub.3 and TeI.sub.2. It
will be appreciated that the component metal species may have
different oxidation states in the various above-mentioned
compounds.
The above listing of precursors, in reference to the digermanes,
germane ring compounds and Ge(II) compounds identified above, may
further include corresponding analogs wherein Ge is replaced by Sb
or Te. Likewise, the above listing of precursors, in reference to
the Sb compounds identified above, may further include
corresponding analogs wherein Sb is replaced by Ge or Te.
Various of the above compounds, e.g., antimony compounds of group
(viii), are light-sensitive in character and amenable to
light/UV-activated processes for PCM deposition. Such compounds
thus may be exposed to radiation for activation during the
deposition, involving visible light exposure or ultraviolet light
exposure.
The deposition may be carried out in a chamber of a deposition
reactor, as a deposition tool that is arranged and adapted for
production of PCM products. The invention contemplates the
provision of doping of the deposited PCM material, with dopant
species that improve the character of the deposited material for
PCM applications. For example, oxygen doping may be employed, or
doping with other implanted species, to provide PCM films of
superior character. The invention also contemplates the in situ
doping of the PCM material at the time of its formation on the
substrate.
A still further aspect of the invention relates to a system for
fabricating a phase change memory device including a phase change
memory material on a substrate, such system including a deposition
tool adapted to receive precursors from precursor supply packages,
and precursor supply packages containing precursors for forming a
phase change memory chalcogenide alloy under conditions producing
deposition of the chalcogenide alloy on the substrate, wherein such
deposition tool is adapted for chemical vapor deposition or atomic
layer deposition operation under conditions comprising deposition
temperature below 350.degree. C.
The chalcogenide metal and alloy precursors described above have
been discovered to provide superior deposition when utilized in CVD
and ALD processes, with lower deposition temperatures employed in
the CVD or ALD process than have heretofore been achievable using
physical vapor deposition techniques. Such lower temperature
deposition capability in CVD and ALD processes is realized as a
result of the chalcogenide metal or metal alloy compound undergoing
beta hydrogen elimination reaction in the CVD and ALD deposition
processes, e.g., involving iso-propyl and/or t-butyl groups. The
digermane compositions benefit from the low bond energy of Ge--Ge.
The Ge(II) compounds are easier to reduce than Ge(IV)
compounds.
The chalcogenide metal or metal alloy precursors for the PCM
material deposition may be provided in any suitable form, including
solids, liquids and gases, and multiphase compositions, depending
on the specific precursors involved. The precursors can be
delivered to the deposition chamber, for carrying out CVD or ALD
therein, by any suitable delivery techniques, dependent on their
phase characteristics, required flow rate, temperature, etc.
Co-reactants may be employed with the precursors to effect the CVD
or ALD operation.
The precursor and co-reactant species can be supplied from material
storage and dispensing packages of any suitable type, depending on
the phase and the material characteristics of the precursor
involved. For example, the storage and dispensing packages may
include supply vessels of a type commercially available from ATMI,
Inc. (Danbury, Conn., USA) under the trademarks SDS, VAC, SAGE or
ProE-Vap. The storage and dispensing packages in preferred practice
can comprise sub-atmospheric pressure systems providing improved
safety and cost of ownership character, in relation to conventional
high pressure material sources, such as the aforementioned packages
available under the SDS, VAC and SAGE trademarks.
In such system and method, at least one of the precursors can be
delivered for the contacting from a storage and dispensing vessel
containing at least one of physical adsorbent, a gas low pressure
regulator, a heat transfer structure, or an ionic liquid. The
storage and dispensing vessel advantageously is adapted to contain
precursor at sub-atmospheric pressure.
For example, the precursor when in a solid or liquid form can be
volatilized to form a precursor vapor which then is flowed to the
deposition chamber and contacted with the substrate on which the
PCM device is to be fabricated. The substrate in such instance can
be suitably heated, by a susceptor or other heating arrangement,
whereby the contact between the precursor vapor and the substrate
results in the deposition of a PCM material, e.g., in a film, on
the substrate. As used in such context, the term "film" means a
layer of the PCM material that is below 1 micrometer in
thickness.
In the delivery operation associated with the CVD or ALD process,
wherein the precursors are in a liquid state, separate bubblers or
other delivery equipment can be employed for each precursor. Liquid
injection of mixtures of precursors can be advantageously employed
to manage disparate volatilities of the different precursors and to
deliver precise volumetric flows of precursor medium having a
desired composition. In the precursor delivery, the precursors may
be utilized in the form of neat liquids, or precursor/solvent
mixtures may be employed, in which the precursor is dissolved or
suspended in a compatible solvent medium. Suitable solvents for
such purpose can be identified by solubility and compatibility data
for the precursor(s) of interest, or by routine solvent screening
determinations, within the skill of the art, based on the
disclosure herein.
The PCM material is deposited on the substrate by CVD or ALD
techniques, in accordance with the invention.
When chemical vapor deposition is employed to form the PCM material
layer on the substrate, continuous CVD in a thermal mode may be
employed, with the CVD operation being conducted in a suitable CVD
reactor chamber. The precursor vapor can be delivered in a carrier
gas stream including the precursor vapor, and a carrier gas such as
hydrogen, or other reducing gas, or an inert gas, or an oxidant, as
may be desirable in a specific application.
When atomic layer deposition or pulsed deposition is used, a dose
step involving introduction of the precursor vapor is alternated
with injection into the deposition chamber of a co-reactant. The
co-reactant can be of any suitable type, as effective to provide a
PCM material layer of desired character on the substrate.
In one embodiment, the alternatingly introduced co-reactant is a
hydrogen plasma, or other plasma co-reactant.
Alternatively, other activation techniques can be employed, such as
ultraviolet (UV) radiation or other light source "tuned" to the
precursor to effect the deposition of the desired PCM material.
Light used for such purpose can be continuous with the precursor
introduction, or may be dosed separately into the deposition
chamber to avoid gas-phase reactions.
The pulsed introduction of reagents into the deposition chamber in
atomic layer deposition operation can include introduction of a
reductive co-reactant in alternation with the introduction of the
metal or metal alloy precursor. The reductive co-reactant may for
example include GeH.sub.4.
The invention further contemplates use of a reductive co-reactant
that is activatable by radiation exposure. Further, in ALD
processes in accordance with the invention, the precursor for
formation of the PCM material on the substrate is alternatingly
pulsed into the deposition chamber. Thus, in instances in which the
PCM material is deposited on a substrate in a pulsed introduction
for contacting the substrate, it may be advantageous in some
embodiments to utilize radiation to activate the PCM material
and/or a co-reactant, e.g., to pulse the radiation source so that
the PCM material or co-reactant are activated. Alternatively, if
both PCM material and the co-reactant are radiation-activatable,
then it may be desirable to maintain radiation generation and
exposure throughout the deposition operation. As a still further
variation, it may be desirable in some instances to pulse the
radiation so that the radiation source is pulsed on when the
precursor is not turned on.
The specific deposition conditions (e.g., temperature, pressure,
flow rate, composition, etc.) for the CVD or ALD operation that is
employed to form the PCM layer on the substrate can be readily
determined within the skill of the art, based on the disclosure
herein. CVD and ALD systems and techniques generally applicable to
the present invention are more fully described in U.S. Provisional
Patent Application 60/791,299 filed Apr. 12, 2006 for "PRECURSOR
COMPOSITIONS FOR ATOMIC LAYER DEPOSITION AND CHEMICAL VAPOR
DEPOSITION OF TITANATE DIELECTRIC FILMS," the disclosure of which
hereby is incorporated herein by reference, in its entirety.
In another specific aspect, the invention relates to low
temperature deposition of germanium-antimony-tellurium (Ge--Sb--Te,
or "GST") material on substrates by a halide precursor
approach.
More specifically, the invention in such aspect relates to a method
of forming a germanium-antimony-tellurium phase change memory
material on a substrate, comprising contacting the substrate with
precursors for a phase change memory germanium-antimony-tellurium
alloy under conditions producing deposition of the
germanium-antimony-tellurium alloy on the substrate, wherein such
conditions comprise temperature below 350.degree. C. and such
contacting comprises chemical vapor deposition or atomic layer
deposition, with the precursors comprising at least one halide
precursor.
Germanium, antimony and tellurium halides are volatile, and
usefully employed for depositing GST thin films. In particular,
their iodides are volatile and the corresponding metal-iodine bonds
are weak. Accordingly, GeI.sub.4, SbI.sub.3 and TeI.sub.2 are
preferred halide source reagents for formation of GST films by CVD
or ALD, e.g., using solid precursor delivery techniques.
Alternatively, one or two of the respective (Ge, Sb, Te) metals can
be supplied from an iodide or other halide precursor compound(s),
and the other one(s) of the metals can be supplied from alkyl metal
compound(s). By way of specific illustrative example, the
precursors can include GeI.sub.4 and TeI.sub.2 as halide precursors
and Sb(CH.sub.3).sub.3 as an alkyl precursor, to form the GST layer
on the substrate. In such halide/alkyl precursor scheme, the
alkyl(s) function as reducing agent(s) to eliminate iodo-methane,
thereby enabling the achievement of clean GST films at low
temperature.
The precursor delivery and deposition conditions can be readily
determined, as appropriate for a given application of forming a GST
material on a substrate, by simple empirical determination, to
identify suitable temperatures, pressures, flow rates and
concentrations to be employed for formation of suitable GST
deposits on the substrate.
Thus, the invention contemplates a system for fabricating a
germanium-antimony-Tellurium phase change memory device including a
germanium-antimony-tellurium phase change memory material on a
substrate, such system comprising a deposition tool adapted to
receive precursors from precursor supply packages, and precursor
supply packages containing germanium, antimony and tellurium
precursors for forming a germanium-antimony-tellurium phase change
memory chalcogenide alloy under conditions producing deposition of
the chalcogenide alloy on the substrate, wherein the deposition
tool is adapted for chemical vapor deposition or atomic layer
deposition operation under conditions comprising deposition
temperature below 350.degree. C., and at least one of the precursor
supply packages contains a halide precursor.
Substrates in the general practice of the present invention can be
of any suitable type, and may be doped or undoped, semiconducting,
semi-insulating, or of other suitable character for the device
structure of the PCM product. Useful substrates in specific
applications may include silicon, sapphire, gallium arsenide,
gallium nitride, silicon carbide, and the like.
Referring now to the drawings, FIG. 1 is a schematic representation
of a phase change memory device 10 comprising a phase change memory
material film 14 formed on a substrate 12, according to one
embodiment of the invention. The film 14 may comprise a
germanium-antimony-tellurium (GST) film, and the substrate may
comprise any suitable substrate compatible with such film.
FIG. 2 is a schematic representation of a process installation 100
including a deposition tool 120 for depositing a phase change
memory material on a substrate in accordance with one embodiment of
the invention, from respective precursor supply packages 102, 104
and 106 of germanium precursor (in vessel 102 labeled "Ge)),
antimony precursor (in vessel 104 labeled "Sb") and tellurium
precursor (in vessel 106 labeled "Te"). Each of the precursor
supply packages includes a storage and dispensing vessel equipped
with a valve head assembly including a flow control valve that may
be manually or automatically operated, to dispense the appertaining
precursor on demand at a desired flow rate.
As illustrated, each of the precursor supply vessels is coupled
with flow circuitry for delivery of the dispensed precursor to the
tool 120. Thus, the germanium precursor supply package 102 is
coupled to the tool by line 110, the antimony precursor supply
package 104 is coupled to the tool by line 112, and the tellurium
precursors supplied package 106 is coupled to the tool by line 114.
The tool can comprise a chemical vapor deposition (CVD) tool, an
atomic layer deposition (ALD) tool, or other suitable tool adapted
to receive the respective precursors and to form a PCM alloy film
on a substrate, in the fabrication of a corresponding PCM
device.
Another aspect of the invention relates to dopants in GeSbTe
semiconductors, which can be formed in polycrystalline form and
thereby accommodate a wider range of stoichiometries and dopants
than typical semiconductors. Doping with nitrogen from levels of a
few tenths of 1% to a few percent can be beneficial to properties
of such materials in specific applications. Although the following
discussion is directed primarily to nitrogen as the dopant species,
it will be appreciated that the invention is not thus limited, and
extends to the use of other dopant species.
Doping may be carried out by use of a reactant gas such as ammonia,
or a vaporizable liquid such as an amine, to introduce nitrogen
into the film. The reaction gas may be introduced separately, as a
co-reactant, or it may be used as a carrier for the precursor(s),
in which case it may also act as a stabilizing agent for the
precursor. If this reactant gas reacts in the gas phase with the
precursor(s), it may be necessary to pulse it alternately with the
precursor(s), optionally with purge steps between pulses. Such
pulsing may also be beneficial if it is desirable to have
non-homogeneous layers, in order to achieve different dopant
concentrations in contact with one or more electrodes for physical
(sticking layer) or electrical (fermi layer adjustment)
purposes.
Doping may also be affected by incorporation of nitrogen from a
precursor. Process adjustments, such as conducting the deposition
in certain "process windows" of reactor pressure, temperature,
and/or gas flow can be employed to control the amount of N
incorporated, thereby enabling adjustment of doping parameters.
Specific precursors for one or more of Ge, Sb and Te materials may
be employed for such purpose.
In another approach, specific co-reactants are employed to induce
reaction pathways with one or more of the precursors that lead to
the desired level of N incorporation. By way of example, use of
NH.sub.3 as a coreactant can be employed to enable lower
temperature deposition and to promote N incorporation into the GST
layer, compared to using H.sub.2 as a co-reactant.
Another aspect of the invention relates to tellurium complexes with
beta-diketiminate ligands, which overcome the problems that many
tellurium precursors used in deposition applications are very
oxygen-sensitive and light-sensitive, and have an unpleasant odor.
By base stabilization with beta-diketiminate ligands, a tellurium
precursor is obtained of a highly stable character with improved
handling and shelf life characteristics, reduced odor, and
sufficient volatility for deposition applications.
The tellurium diketiminate complexes of the invention can be used
for CVD/ALD to form Te or Te-containing films. These compounds can
be used in combination with Ge- and/or Sb-compounds to produce
Te--Ge--, Te--Sb-- or Ge--Sb--Te films in varied compositions. A
general procedure to synthesize diketiminate ligands has been
described in the literature, but such procedure is disadvantageous,
since very bulky aryl substituents on the coordinating nitrogen
atoms are required.
In contrast, we have discovered that smaller alkyl ligands as
iso-propyl, n-butyl, tert-butyl or amine-substituted alkyl groups,
as for example ethylene-dimethylamine, can be advantageously used
to produce superior tellurium diketiminate precursors for CVD/ALD
applications. Smaller substituents on the nitrogen donor atoms
provide sufficient volatility to form good films at low
temperature.
The ligands L can be used as the lithium salt or in a free imine
form to synthesize the desired Te complexes. The lithium salt of
the ligand can be reacted with TeX.sub.4 (wherein X=Cl, Br, I) to
generate LTeX.sub.3 by salt elimination, which can then be reacted
with either a lithium or a Grignard reagent to produce LTeR.sub.3
(wherein R=alkyl, aryl, amide, silyl).
Alternatively the free imine form of the ligand L can be reacted
with a tellurium organic compound such as TeMe.sub.4 to produce the
desired Te species LTeMe.sub.3 by methane elimination. The
diketiminate ligands provide very effective base stabilization of
the reactive metal center tellurium. The invention therefore
provides a new class of Te complexes that provide greater stability
and shelf life, while retaining sufficient volatility to form
superior Te films via CVD/ALD at low temperatures.
The tellurium complexes of the invention have the formulae (I) and
(II):
##STR00001## wherein R.sub.1, R.sub.2 and R.sub.3 they be the same
as or different from one another, and each is independently
selected from C.sub.1-C.sub.6 alkyl, C.sub.6-C.sub.10 aryl, silyl
and C.sub.1-C.sub.12 alkylamine (which includes both monoalkylamine
as well as dialkylamine); and
##STR00002## wherein R.sub.1, R.sub.2 and R.sub.3 they be the same
as or different from one another, and each is independently
selected from C.sub.1-C.sub.6 alkyl, C.sub.6-C.sub.10 aryl, silyl
and C.sub.1-C.sub.12 alkylamine (which includes both monoalkylamine
as well as dialkylamine).
The beta-diketiminate ligands may for example be synthesized by the
following procedure:
##STR00003##
The tellurium complexes then can be synthesized by the following
reaction:
##STR00004## or alternatively by the following synthesis
reaction:
##STR00005## or by the following synthesis reaction:
##STR00006##
The tellurium complexes of the invention are usefully employed as
CVD/ALD precursors for deposition of tellurium-containing thin
films, e.g., by liquid injection of neat precursor material, or in
organic solvent or by direct evaporation.
The invention in another aspect relates to germanium complexes and
their use in CVD/ALD for forming germanium-containing films, e.g.,
GST films, wherein the germanium complexes are selected from
among:
##STR00007## wherein the R groups in the second formula may be the
same as or different from one another, and each is independently
selected from among H, C.sub.1-C.sub.6 alkyl, C.sub.6-C.sub.10
aryl, C.sub.3-C.sub.8 cycloalkyl, heteroatom groups, and other
organo groups.
Another aspect of the invention relates to digermane and strained
ring germanium precursors for CVD/ALD of germanium-containing thin
films. Previously employed germanium precursors such as germane
that have been used for forming GST (germanium-antimony-tellurium)
films for phase change memory devices require very high temperature
deposition conditions. This in turn makes it difficult to form a
pure Ge.sub.2Sb.sub.2Te.sub.5 phase material. The present invention
overcomes this deficiency in the provision of precursors having a
high vapor pressure at ambient conditions, which are useful to
deposit germanium-containing films at temperatures below
300.degree. C.
Germanium-germanium bonds are inherently weak (.about.188 kJ/mole)
and become less stable with electron withdrawing substituents such
as chlorine or NMe.sub.2. Such bonds can readily dissociate to form
R.sub.3Ge radicals under UV photolysis or thermolysis, or by
chemical oxidation using peroxides, ozone, oxygen or plasma.
Commercially available digermanes include hydride, methyl, phenyl,
or ethyl groups that require high temperatures for decomposition
and the resulting films are often contaminated with carbon
residues.
We have overcome such deficiency by the provision of germanium
complexes using as ligands isopropyl, isobutyl, benzyl, allyl,
alkylamino, nitriles, or isonitriles to achieve complexes that
enabled the deposition of pure germanium metal films at low
temperatures. In addition, the invention contemplates strained-ring
germanium complexes (e.g., germacyclobutane) that can undergo
thermal ring opening to generate a diradical intermediate that
readily dissociates to germylene fragments. The bond dissociation
energy of the strained Ge--C bond (63 kcal/mol) is considerable
lower than Ge--CH.sub.3 (83 kcal/mol), thereby enabling lower
temperature film deposition of germanium to be achieved, than has
been achievable with the aforementioned conventional germanium
precursors.
The germanium complexes of the invention include those of formulae
(I)-(III) below:
(I) alkyldigermanes of the formula
##STR00008## wherein each R may be the same as or different from
the others, and each is independently selected from among
isopropyl, isobutyl, benzyl, allyl, alkylamino, nitriles, and
isonitriles; (II) alkyl(dialkylamino)germanes of the formula
.sub.x(R.sub.2R.sub.1N)R.sub.3-xGe--GeR'.sub.3-y(NR.sub.1R.sub.2).sub.y
wherein each R may be the same as or different from the others, and
each is independently selected from among isopropyl, isobutyl,
benzyl, allyl, alkylamino, nitriles, and isonitriles; and (III)
strained-ring germane complexes of the formula:
##STR00009## wherein each of R.sub.1, R.sub.2, R.sub.3 and R.sub.4
may be the same as or different from the others, and each is
independently selected from among H, C.sub.1-C.sub.6 alkyl,
C.sub.6-C.sub.10 aryl, C.sub.3-C.sub.8 cycloalkyl, or a heteroatom
group.
##STR00010##
Illustrative synthesis processes that can be employed for forming
germanium complexes of formula (III) includes the following:
##STR00011##
The strained ring alkylgermanes are usefully employed as CVD/ALD
precursors for forming germanium-containing thin films on
substrates involving reactions such as those illustratively shown
below.
The complexes (I) can be synthesized, by way of example, according
to the following synthesis process:
##STR00012## or by the following synthesis:
##STR00013## or by a synthesis such as the following:
##STR00014## or a synthesis procedure such as:
##STR00015##
The germanium complexes of formula (II) can be formed by the
following illustrated procedure:
Strained Ring Alkylgermanes as Cvd/ALD Precursors for Thin Metal
Films
##STR00016##
Another aspect of the invention relates to a single-source
precursor for germanium and tellurium, as useful in the formation
of GST films. Such single-source of germanium telluride precursors
may be used in combination with an antimony precursor for GST film
formation, optionally with co-reactants as may be desirable to
provide films of appropriate stoichiometry for a given
application.
The germanium telluride complexes of the invention in one aspect
include dialkylgermanetellurones. Suitable dialkylgermanetellurones
can be synthesized by oxidative addition reaction of germanium (II)
dialkyls with elemental tellurium powder in a solvent medium such
as tetrahydrofuran (THF). In some instances so it may be desirable
to conduct the reaction in the absence of light, depending on the
light-sensitivity of the product germanium-tellurium complex. An
illustrative synthesis procedure is set out below:
##STR00017##
The single-source Ge--Te precursors of the invention can be
advantageously used to facilitate lower temperature deposition
processes or to increase GST film growth rates in specific
applications.
Germanium tellurides of the invention, in another embodiment, can
be formed by the following synthesis procedure:
Germanium Telluride ALD/CVD Precursors
##STR00018##
Other germanium telluride complexes can be formed by the following
synthesis process:
##STR00019## or by the following generalized reactions:
R.sub.3GeM+R'.sub.nEX.fwdarw.R.sub.3Ge-ER'.sub.n
R.sub.3GeX+R'.sub.nEM.fwdarw.R.sub.3Ge-ER'.sub.n
R.sub.3Ge--X+NaTeR'.fwdarw.R.sub.3Ge--TeR' wherein E is tellurium;
M is Li, Na, or K, X is chlorine, bromine or iodine; and the R and
R' groups may be the same as or different from one another, and
each is independently selected from among H, C.sub.1-C.sub.6 alkyl,
C.sub.6-C.sub.10 aryl, C.sub.3-C.sub.8 cycloalkyl, heteroatom
groups, and other organo groups.
One Ge--Te complex of the invention is:
##STR00020## wherein each of the R substituents may be the same as
or different from one another, and is independently selected from
among H, C.sub.1-C.sub.6 alkyl, C.sub.6-C.sub.10 aryl,
C.sub.3-C.sub.8 cycloalkyl, heteroatom groups, and other organo
groups.
It will therefore be seen that the present invention contemplates a
variety of precursors suitable for use in forming phase change
memory films, e.g., GST films, and that the various precursors of
the invention include precursors enabling deposition of films via
CVD/ALD processes at temperatures below 300.degree. C., as well as
Ge--Te precursors affording substantial advantage in forming
germanium- and tellurium-containing films.
While the invention has been has been described herein in reference
to specific aspects, features and illustrative embodiments of the
invention, it will be appreciated that the utility of the invention
is not thus limited, but rather extends to and encompasses numerous
other variations, modifications and alternative embodiments, as
will suggest themselves to those of ordinary skill in the field of
the present invention, based on the disclosure herein.
Correspondingly, the invention as hereinafter claimed is intended
to be broadly construed and interpreted, as including all such
variations, modifications and alternative embodiments, within its
spirit and scope.
* * * * *